Method for injection molding a plastic part using a film gate

Abstract

A method and apparatus for injection molding a plastic part using a film gate. The film gate is constructed of a pair of tenon members which retract into a mortise tooled into a mold section. Because the tenon members extend to release the dross formed in the runner, the film gate may be placed in the center of the mold section to decrease the pressure gradient in the curing plastic and to allow the gate to be located where aesthetic aberrations, from the removal of the dross, will not be a problem in the finished article.

I claim: 
     
       1. A method for injection molding a plastic part comprising: (a) providing a first mold section with a mortise formed in said first mold section;   (b) providing a second mold section which when lowered into sealed engagement with said first mold section forms a mold cavity;   (c) providing a sprue running through said first mold section and opening into said mortise of said first mold section;   (d) providing at least one tenon member which when inserted into said mortise of said first mold section forms a runner and a film gate through which a plastic material can pass from said sprue into said mold cavity;   (e) retracting said tenon member into a generally flush engagement with said first mold section thereby forming said runner and said film gate;   (f) clamping said first mold section and said second mold section together to form said mold cavity;   (g) injecting said plastic material through said sprue;   (h) forcing said plastic material through said runner and said film gate into said mold cavity;   (i) curing said plastic material within said mold cavity;   (j) unclamping said first mold section and said second mold section;   and   (k) extending said tenon member a sufficient distance to eject the finished plastic article from said first mold section with said tenon member.   
     
     
       2. The method according to claim 1, wherein said extension of said tenon member allows the removal from said first mold section of dross formed in said runner. 
     
     
       3. The method according to claim 1, wherein said tenon member is retracted by a hydraulic piston mounted to said first mold section and connected to said tenon member. 
     
     
       4. The method according to claim 1, wherein said tenon member is retracted by a plurality of hydraulic pistons mounted to said first mold section and connected to said tenon member. 
     
     
       5. The method according to claim 1 wherein said tenon member consists of a dovetailed metal bar tooled so that a corner of said bar is concavely chamfered to form said runner and a side of said bar is tooled to provide said film gate through which plastic material may pass from said sprue to said mold cavity. 
     
     
       6. The method according to claim 1, wherein said tenon member is retracted by a hydraulic piston mounted to a support bracket secured to said first mold section and connected to said tenon member. 
     
     
       7. The method according to claim 1, wherein said tenon member is retracted by a plurality of hydraulic pistons mounted to a support bracket secured to said first mold section and connected to said tenon member. 
     
     
       8. The method according to claim 7, further comprising providing guide pin support rods mounted to said first mold section along which said tenon member moves into and out of engagement with said mortise of said first mold section. 
     
     
       9. The method according to claim 8, further comprising providing a guide pin support mounted to said first mold section and securing said guide pins in proper alignment with said tenon member so that said tenon member may slide into and out of engagement with said mortise of said first mold section. 
     
     
       10. The method according to claim 9, wherein said guide pin supports are of a generally home-plate configuration. 
     
     
       11. The method according to claim 1, further comprising the step of heating the plastic material as the material passes through the runner. 
     
     
       12. The method according to claim 1, further comprising the step of heating the plastic material as the material passes through the sprue. 
     
     
       13. The method according to claim 1, further comprising the step of providing a plurality of tenon members which fit into substantially flush engagement with said mortise of said first mold section. 
     
     
       14. The method according to claim 1, further comprising the step of locking said tenon member with locking means to said first mold section during tile molding process. 
     
     
       15. The method according to claim 14, wherein said locking means comprise hydraulic pistons mounted on said first mold section and piston receiving slots located on said tenon member. 
     
     
       16. A method for injection molding a plastic part comprising: (a) providing a first mold section with a mortise formed in said first mold section;   (b) providing a second mold section which when lowered into sealed engagement with said first mold section forms a mold cavity;   (c) providing a sprue running through said first mold section and opening into said mortise of said first mold section;   (d) providing at least one tenon member which when inserted into said mortise of said first mold section forms a runner and a film gate through which a plastic material can pass from said sprue into said mold cavity;   (e) retracting said tenon member into a generally flush engagement with said first mold section thereby forming said runner and said film gate;   (f) clamping said first mold section and said second mold section together to form said mold cavity;   (g) injecting said plastic material through said sprue;   (h) forcing said plastic material through said runner and said film gate into said mold cavity;   (i) curing said plastic material within said mold cavity;   (j) unclamping said first mold section and said second mold section; and   (k) removing the finished plastic article and plastic hardened in said runner from said first mold section as a single integrally molded piece.   
     
     
       17. A method for injection molding a plastic part comprising: (a) providing a first mold section having an injection surface and a molding surface with a mortise formed in said first mold section and dividing said molding surface;   (b) providing a second mold section which when lowered into sealed engagement with said first mold section forms a mold cavity;   (c) providing a sprue running from said injection surface of said first mold section to said mortise formed in said first mold section;   (d) providing at least two tenon members each having a surface which when said tenon members are inserted into said mortise form a runner and a film gate between the tenon member surfaces;   (e) retracting said tenon member into a generally flush engagement with said first mold section thereby forming said runner and said film gate dividing said molding surface of said first mold section;   (f) clamping said first mold section and said second mold section together to form said mold cavity;   (g) injecting said plastic material through said sprue;   (h) forcing said plastic material through said runner and said film gate into said mold cavity;   (i) curing said plastic material within said mold cavity;   (j) unclamping said first mold section and said second mold section;   (k) extending said tenon member a sufficient distance to release a portion of plastic material hardened within said runner and said film gate; and   (l) withdrawing the finished plastic article from said first mold section.